1. Field of the Invention
The prevent invention relates to a photosensitive member formed by stacking in order a photoconductive layer containing amorphous Si and a surface protective layer, and to an image forming apparatus represented by an electrophotographic apparatus comprising the photosensitive member of the present invention.
2. Related Background Art
In the electrophotographic apparatus such as a copier, a facsimile, a printer or the like, an outer peripheral surface of the photosensitive member disposed with a photoconductive layer on its surface is uniformly charged by charging means such as corona charging, roller charging, fur brush charging, magnetic brush charging or the like and then the image of an object to be copied is exposed by laser or LED responding to a reflective light or a modulation signal, whereby an electrostatic latent image is formed on the outer peripheral surface of the above described photosensitive member. Further toner is adhered on the photosensitive member and then it is transferred to a copy paper or the like to complete copy.
After completing copy in this way by the electrophotographic apparatus, because toner remains on the outer peripheral surface of the photosensitive member, it is necessary to remove the remained toner. The removal of such remained toner is usually performed by a cleaning step using a cleaning blade, a fur brush, a magnetic brush or the like.
Also, in recent years, from the environmental concern, for the purpose of reducing or canceling waste toner, an electrophotographic apparatus omitting a cleaning equipment is proposed and disclosed. This system is a direct charger similar to a brush charger such as disclosed in Japanese Patent Application Laid-Open No. 6-118741 which serves as a cleaning step, or a developing device such as disclosed in Japanese Patent Application Laid-Open No. 10-307455 which serves as a cleaning step, or the like, but each system includes a step of rubbing the toner and the photosensitive member surface together to remove the toner.
Since the amorphous silicon photosensitive member has a large surface hardness and a small wear amount, a low resistance material contained in a charging product and a transfer paper is difficultly removed in the above described cleaning step from the photosensitive member, whereby the electrophotographic apparatus using the photosensitive member easily generates a high-humidity smearing, and efforts for preventing this has been still continued since from the past. Concretely, in order to remove a moisture content by heating with a heater, removal of a substance causing the smearing by rubbing means and use of a surface protective material which is difficultly oxidized or adhered by the substance causing the smearing or the like are enumerated, which show an effect.
However, with recent rapid advancement of digitalization, when an image is created by collection of fine dots, the high-humidity smearing tends to appear particularly in a half-tone image. This necessitates further an improved performance.
For one of replies as the measure to prevent the high-humidity smearing concerning the present invention, as disclosed in Japanese Patent Application Laid-Open No. 9-204056, there is proposed a method wherein in a photosensitive member having amorphous silicon as its sensitive layer, the carbon amount of the surface of an electroconductive substrate which forms the photosensitive layer is increased so as not to be oxidized but easy to wear out the surface and at the same time the smoothness of the surface is enhanced so that removal of the substance causing the high-humidity smearing is made easy. This is defined by a value of the surface roughness measured by a surface roughness tester.
Also, in Japanese Patent Application Laid-Open No. 10-333350, there is disclosed a method wherein the photosensitive surface is polished inside the electrophotographic apparatus and the surface thereof is made flat, thereby achieving the same effect.
Further, with improvement of recent high picture quality of printed images, the toner having an average particle size smaller than the conventional one or the toner having a low melting point corresponding to an energy saving has come to be used, and not only in the above described cleaning step but also in a toner removal step performed at the same time with other steps, removal of the remained toner becomes difficult, and repeated copying sometimes leads to a problem of toner adherence wherein the remained toner adheres to the photosensitive member surface and thereby an image defect having a black point or a white point in the image is generated.
As a measure for solving the above described problem, as disclosed in Japanese Patent Application Laid-Open No. 9-297420, there is proposed a method of previously making rough the surface of the electroconductive substrate on which the sensitive layer is formed by cutting or a rotary ball mill equipment, in the photosensitive member having amorphous Si as its sensitive layer. The surface of the substrate is regulated by a value of the surface roughness of xcexcm order measured by the surface roughness tester.
Also, in Japanese Patent Application Laid-Open No. 8-129266, a value of the surface roughness Ra is regulated. However, this regulates a processing shape of the electroconductive substrate and the substrate surface is regulated by a value of the surface roughness of xcexcm order measured by the surface roughness tester.
However, due to the from recent advancement of digitalization of the electrophotographic apparatus and enhanced awareness of ecology, while the fact that an amorphous photosensitive member is still used, prolongation of the life of the photosensitive member and an energy saving are further required.
Concretely, the attempt of raising the life of the photosensitive member of a low speed, a medium speed printer for personal use or the like to the level equal to or more than the life of the main apparatus, reducing a waste material and abolishing the use of a photosensitive member heater of a high speed printer for office use or the like while maintaining its life at a level equal to or more than the life of the main apparatus are required.
For this purpose, the photosensitive member is required to have such a constitution as to prevent the high-humidity smearing without depending on a wear or a polish which imposes a limit to the life of the photosensitive member, that is, to satisfy all the above even when the photosensitive member heater is abolished.
Also, in recent years, accompanied by advancement of digitalization of an electrophotographic apparatus, a latent image formation by a light source mainly comprising a single wavelength is becoming the mainstream. This sometimes leads to a problem that the above proposed method of cutting the substrate in advance causes a difference in an incident exposure amount to photoconductive layers due to the substrate shape and as a result a stripe pattern is generated on the printed image. Also, in order to prevent an interference fringe by reflection of light which reaches the substrate, the establishment of a new step of previously making the surface of the electroconductive substrate rough leads to a high cost. On the contrary, when the substrate is processed within the range of roughness where the above described stripe pattern is not generated, the toner adherence can not be sufficiently inhibited.
An object of the present invention is to provide an electrophotographic photosensitive member and an electrophotographic apparatus capable of preventing a high-humidity smearing and forming an excellent image.
Another object of the present invention is to provide a photosensitive member and an image forming apparatus which prevents the high-humidity smearing at the time of cleaning and achieves the excellent image formation.
Still another object of the present invention is to provide a photosensitive member and an image forming apparatus which prevents the toner adherence at the time of cleaning and achieves the excellent image formation.
A further object of the present invention is to provide an electrophotographic photosensitive member comprising a photoconductive layer containing at least amorphous Si and a surface protective layer which are stacked in order on an electroconductive substrate, wherein the electrophotographic photosensitive member has a difference in the height of concave and convex corresponding to 90% and 50% of the cumulative frequency of the concave and convex within the range of 3 nm to 200 nm with the most deepest point of the surface roughness concave and convex within the range of 10 xcexcmxc3x9710 xcexcm of the above described photosensitive member as a standard.
A still further object of the present invention is to provide an image forming apparatus comprising:
an electrophotographic photosensitive member comprising a photoconductive layer containing at least amorphous Si and a surface protective layer which are stacked in order on an electroconductive substrate, wherein the member has a difference in the height of concave and convex corresponding to 90% to 50% of the cumulative frequency of the concave and convex height within the range of 3 nm to 200 nm with the most deepest point of the surface roughness concave and convex within the range of 10 xcexcmxc3x9710 xcexcm of the above described photosensitive member as a standard;
charging means for the photosensitive member;
exposing means for forming an electrostatic image; and
developing means for visualizing the latent image.
As a result of the sharp study by the present inventors, it was revealed that the effect of preventing the high-humidity smearing is not necessarily deteremined by macroscopic substrate surface roughness but rather largely depends on inherent microscopic (concretely, from several nm to several tens nm order) surface roughness of the amorphous silicon film.
It was also revealed that the effect of preventing the toner adherence is not necessarily determined by the substrate surface roughness of xcexcm order measured by the surface roughness tester, but rather largely depends on the inherent microscopic (concretely, from several nm to several tens nm order) surface roughness of the amorphous Si film.
That is, it became clear that film formation in the shape having a few, shallow valleys between mountains (convex portions) at the time of growth of the amorphous silicon film immediately prevented the high-humidity smearing from the beginning and maintained an excellent level.
Further it was concluded that the macroscopic roughness, that is, a substrate cutting processing, a plastic processing or the like are preferably appropriately selected for the purpose of preventing the melting, the toner adherence or the like and maintaining separation stability, and even in this case, when the film is formed under the microscopic surface roughness condition as proposed by the present invention, the high-humidity smearing can be prevented from the beginning.
The separation stability as described here is referred to as stability of a step for separating a transfer material from the photosensitive member after the photosensitive member and the transfer material are brought into contact so that the toner on the photosensitive member surface is moved to the transfer material. Concretely, the toner once transferred to the transfer material will never return to the photosensitive member again, and the degree of a state where the transfer material is excellently separated and no paper jamming is generated is expressed by a paper jamming rate (hereinafter referred to as xe2x80x9cjamming ratexe2x80x9d). According to the study by the present inventors, for the purpose of maintaining this separation stability, it is preferable that a certain degree of the concave and convex is available on the surface of an a-Si photosensitive member and it is assumed that a surface energy state caused by the gap or the concave and convex formed by the transfer paper and its concave and convex at the time of contacting the transfer paper contributes to the separation stability.
The present inventors found as the result of repeated studies for solving the above described problem that, in the photosensitive member formed by stacking in order the photosensitive layer containing at least amorphous Si and the surface protective layer on an electroconductive substrate, with the most deepest point of the surface roughness concave and convex within the range of 10 xcexcmxc3x9710 xcexcm, to use another expression, the lowest point as a standard, the difference in the height of the concave and convex corresponding to 90% and 50% of the cumulative frequency of the frequency distribution of the concave and convex height is set within the range of 3 nm to 200 nm so that the above described problem can be solved.
As the means for adjusting to a preferable range the difference in the height of the concave and convex corresponding to 90% and 50% of the cumulative frequency of the concave and convex height with respect to the most deepest point, as a standard, of the surface roughness concave and convex within the range of 10 xcexcmxc3x9710 xcexcm according to the present invention, the following method can be used.
There are a method of dry-polishing or wet-polishing to obtain a desired surface roughness by using as a polishing agent a fine powder such as of silica, chromium oxide, titanium oxide, iron oxide, zirconium oxide, diamond, nitrogen carbide, silicon carbide, silicon nitride or cerium oxide; and a method of obtaining a desired surface roughness by buff-polishing, magnetic polishing, magnetic fluid FFF (Fluid assisted Fine Finishing), electrophoresis utilizing FFF, plasma utilizing FFF, EEH (Elastic Emission Hacking) or polishing by use of a lapping film. When the difference in the height of the concave and convex is smaller than a desired value, it can be made lager by using these methods.
FIG. 17A is a schematic representation for showing the polishing apparatus for the surface of an electrophotographic photosensitive member. FIG. 17A, reference numeral 1 denotes an electrophotographic photosensitive drum having a surface layer to be processed on a surface thereof. Reference numeral 2 denotes a polishing tape having a crystal SiC coated on a polishing surface thereof, which is the trade name of Lapping Tape LT-C2000, manufactured by Fuji Film. Reference numeral 3 denotes a cylindrical support for contacting the surface of the photosensitive drum 1 with the polishing tape 2. As the polishing tape used in the present invention, in addition to the tape having crystal SiC coated on its surface, it is preferable to use a tape having a powder such as of iron oxide, alumina or diamond coated on its surface. Reference numeral 4 denotes a pedestal for the cylindrical support 3, which is arranged in parallel to the revolution axis direction of the photosensitive drum 1 and to which a weight 5 is applied as a load. Reference numeral 6 denotes a delivery motor for delivering the polishing tape 2 which is delivered at a constant rate and pulled by a weight 7 to convey at a constant rate. In this case, since the polishing tape is conveyed in the forward direction of revolution of the photosensitive drum, polishing can be conducted without accumulating a polishing powder of SiC and foreign matters in a gap between the polishing tape 2 and the photosensitive drum 1, whereby a desired surface roughness can be obtained. When the surface roughness is larger than a desired value, it can be made smaller by this method.
FIG. 17B is a sectional view taken in the line 17Bxe2x80x9417B of the polishing apparatus of FIG. 17A. The photosensitive drum 1 can move in the direction of its revolution axis (direction of arrows X). The polishing tape 2 and the cylindrical support 3 may be moved. By these operations, two-dimensional polishing can be controlled and therefore a desired surface roughness can be more easily obtained.
That is, it was revealed that, in the photosensitive member formed by stacking in order the photosensitive layer containing at least amorphous Si and the surface protective layer, on an electroconductive substrate with the most deepest point of the surface roughness concave and convex within the range of 10 xcexcmxc3x9710 xcexcm, to use another expression, the lowest point as a standard, the difference in the height of the concave and convex corresponding to 90% and 50% of the cumulative frequency of the frequency distribution of the concave and convex height is set within the range of 3 nm to 35 nm, preferably within the range of 5 nm to 30 nm so that particularly the high-humidity smearing can be inhibited. This led to the completion of the present invention.
Or it was found that, in the photosensitive member formed by stacking in order the photosensitive layer containing at least amorphous Si and the protective layer on an electroconductive substrate, with the most deepest point of the surface roughness concave and convex within the range of 10 xcexcmxc3x9710 xcexcm, to use another expression, the lowest point as a standard, the difference in the height of the concave and convex corresponding to 90% and 50% of the cumulative frequency of the concave and convex height is within the range of 35 nm to 200 nm, preferably within the range of 45 nm to 180 nm so that particularly the toner adherence can be inhibited. This led to the completion of the present invention.
The microscopic surface roughness in the present invention indicates a value of surface roughness Ra measured by an atomic force microscope (AFM) (Q-Scope 250 made by Quesant Corporation) and, for the purpose of measuring the microscopic surface roughness with high accuracy and excellent repeatability, it is desired to be within the measurement range of 10 xcexcmxc3x9710 xcexcm and to be a result measured in such a manner as to avoid an error due to a sample curvature inclination (tilt). Concretely, a correction (parabolic) is enumerated wherein, by a tile removal mode of Q-scope 250 made by Quesant Corporation, the curvature of the AFM image of the sample is allowed to fit with a parabola and then is made flat. The electrophotographic photosensitive member usually takes a cylindrical shape, and therefore this is a preferred technique to be employed. Further, when there remains a tilt in the image, a correction for removing the tilt is performed (line by line). In this way, the tilt of the sample can be appropriately corrected within the range not to cause a distortion in data.
Further, the present inventors found that in addition to the above described surface shape, constituting the photoconductive layer with a plurality of layers expedites an inhibition of the toner adherence.
The fluctuation of the substantial absorption depth of the image exposure caused by a band gap of the photoconductive layer generates fluctuation of the potential of the latent image. This potential fluctuation, concretely the remaining potential and the ghost potential are considered to deteriorate a fog which becomes a core for the toner adherence or freshness of a picture image.
It was also found that by continuously changing the interface compositions of the surface protective layer and the photosensitive layer of the photosensitive member, the control of the toner adherence can be further effectively performed.
It is desirable that a spectral reflectance in the above described interface compositions satisfies the following equation (1):
0xe2x89xa6(Maxxe2x88x92Min)/(Max+Min)xe2x89xa60.4xe2x80x83xe2x80x83(1) 
where, when using light having the range of a wavelength from 450 nm to 650 nm, Min denotes the minimum value of a reflectance (%) and Min denotes the maximum value.
Here, the reflectance of the present invention indicates a value of the reflectance (percent) measured by using a spectrophotometer (MCPD-2 manufactured by OHTSUKA ELECTRON COMPANY). To describe its outline, first, a spectral luminous intensity I (O) of the light source of a spectrograph is taken and next, a spectral reflective light intensity I (D) of a photosensitive member is taken and then a reflectance R=I(D)/I(O) is determined. To measure with high accuracy and excellent repeatability, it is desirable to fix the detector by a jig so that its angle is made constant against the photosensitive member having a curvature.
Concrete examples of the interface control are shown in FIGS. 1A and 1B. The curves A and B in FIG. 1A show example A (value of equation (1): 0.48) and example B (value of equation (1): 0.41), respectively, which are measurement examples in xe2x80x9cthe presence of an interfacexe2x80x9d and are out of the range of the above described equation. The curves C and D in FIG. 1B show example C (value of equation (1): 0.28) and example D (value of equation (1): 0.16), respectively, which are measurement examples in xe2x80x9cthe absence of an interfacexe2x80x9d satisfying the equation according to the present invention. The reason why there are two curves is because of the differences in the film thickness of each surface protective layer, and the wave form moves left and right on the graph responding to the differences in the film thickness. Because the maximum value thereof corresponds to the amplitude of the wave form, in contrast to the absence of the interface, when viewed from a fixed simple wavelength, the presence of the interface largely fluctuates in its reflectance against the fluctuation of the film thickness.
That is, a fine roughness causes the substantial fluctuation of film thickness of a surface protective layer on the picture image exposure incident light path. This fluctuation of the film thickness makes the fluctuation of the sensitivity larger in the presence of the interface than in the absence of the interface, and it is considered that this causes the fog which becomes a core for the toner adherence or deteriorates freshness of the picture image.
(Frequency Distribution of Surface Roughness)
Hereinafter, the frequency distribution of the surface roughness which is an important index of the present invention will be described.
The atomic force microscope (AFM) exceeds 0.5 nm in the horizontal resolution (resolution in a parallel direction to a sample surface) and has 0.01 to 0.02 nm in the vertical resolution (resolution in a vertical direction to the sample surface) and can measure a three dimensional shape of the sample. A significant difference from the surface roughness tester widely used in the past resides in its high resolution.
In the resolution of as much a high degree as this, it is possible to measure not the roughness of an order where the roughness of the photosensitive member substrate is dominant but the roughness originating from the nature of a deposited film itself such as the photoconductive layer and the surface layer.
Although the roughness of the photosensitive member substrate depends on the xe2x80x9cmoldxe2x80x9d such as the above described lathe, the ball mill or a xe2x80x9ctooth shapexe2x80x9d such as a dimple processing and a xe2x80x9cprocessing memberxe2x80x9d, no xe2x80x9cmoldxe2x80x9d exists in the roughness of the deposited film, but there exists a shape factor which can not be sufficiently expressed by Ra (center line average roughness) and Rz (ten points average roughness) merely defined by JIS-B0601. The present inventors thought that the shape factor could be the clue to the above described toner adherence prevention.
Concretely, under various conditions, the amorphous silicon photosensitive layers (all the layers including the interface of each layer such as the preventive layer, the photoconductive layer and the surface layer) are produced on the electroconductive substrate having the surface roughness Ra of 10 nm within the range of the same visual field (10 xcexcmxc3x9710 xcexcm). Then the concave and convex height thereof was measured by the atomic force microscope, and the frequency distribution thereof was determined, compared and studied.
In the same measurement by the conventional surface roughness tester widely used, for example, a contact type surface roughness tester (SE-3400) made by KOSAKA LABORATORY CORPORATION, a significant difference cannot be observed, while the index used by the present invention is considered to be an index showing the characteristics of the material of the amorphous silicon photosensitive member, which draws a clear line of demarcation against the conventional tester.
It should be noted that the present inventors, at the time of the AMF measurement, conducted the measurement of several samples in several scan sizes. The scan size is a length of one side of a square to be scanned, and accordingly a scan size of 10 xcexcm is to scan the range of 10 xcexcmxc3x9710 xcexcm, that is, 100 m2. By taking a graph abscissa as the scan size, a part of the result will be shown in FIG. 2.
FIG. 2 shows two sample films formed on the same substrate under different forming conditions having a relatively small minute roughness and a medium roughness by a measurement visual field and a roughness index JIS-Ra (central line average roughness) which is generally easy to image. In FIG. 2, symbol ▪ shows the sample film having a relatively small minute roughness, and symbol ♦ shows the sample film having a medium roughness.
When the scan size is enlarged, that is, when the measurement range is enlarged, the measurement value is stabilized. However, depending on a substrate swelling of the sample substrate, a peculiar shape such as a projection and an influence of the processed shape, the measurement becomes hard to reflect the minute shape. When an angle of visibility becomes small, selected variations of measurement places become large. Hence, the present invention used a 10 xcexcmxc3x9710 xcexcm visual field which is collectively excellent in measurement detection performance and stability.
From the above described circumstances, the present invention is not limited to the visual field of 10 xcexcmxc3x9710 xcexcm.